The protected members of System.Xml.Serialization.XmlSerializationWriter are intended for use only by derived classes that are used internally within the .NET Framework XML serialization infrastructure.
SOAP encoding allows a unique XML element to appear once within a SOAP message as a multiRef element identified by an id attribute. The id value can be referenced multiple times by href attributes (or ref attributes in SOAP 1.2) in substitute elements.
SOAP encoding is described in Section 5 of the SOAP 1.1 specification.